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CameraLink HS

CameraLink HS has a long history even though the standard itself is
young. With the ever increasing camera speeds "classic" CameraLink
standard is not able to scale easily beyond 850 MB/s, so another new
interface was needed to meet the needs of ever higher bandwidths at
the same or even lower cost.

After an extended search for the optimal technical solution by a body of
leading frame grabber producers, the HS-Link technology from Teledyne
DALSA provided the first "proof of concept" which, in the guise of a
product, was to demonstrate that the proposed concept really worked.
It was decided to use components from the high-speed network
technology to implement bandwidths of up to 300 MB/s with a single
link, or "lane" in CameraLink HS jargon, and up to 6 GB/s with up to
20 lanes.

A complete CameraLink HS core can be integrated in the FPGA making
the integration of the technology cost-effective with a ready-to-use IP
core available to developers.

Particular attention was given to the triggering capability of the
interface by adapting the link layer protocol and the adoption of special
key codes. An extremely low trigger jitter of only 3.2 ns, can be sent from
the frame grabber to the camera, making CameraLink HS excellent for
line scan camera applications where high trigger frequencies can occur
that must be transmitted with little jitter.

To ensure data integrity, CameraLink HS includes a checksum and
resend mechanism that is implemented in hardware on the FPGA and
does not need additional memory capacity in the camera. This delivers
a cost-effective solution with lower resources needed inside the
camera, enabling cameras to be made smaller due to the lower
hardware resources.

Functional diagram of CameraLink HS from a camera perspective

With CameraLink HS, as with CoaXPress, the cameras supply a GenICam
GenApi XML device description. However, unlike CoaXPress, the device
description may not be fully "visible" to the user because CameraLink
HS does not require the use of GenICam GenTL. This means that the
software interface of the camera is provided via the frame grabber
software interface. The use of a GenTL driver for the frame grabber
overcomes this potential issue.

With extremely high data rates a useful feature of CamerLink HS is data
forwarding. Transmitters at the receiving end in the frame grabber can
loop data with relatively little effort and expense. In this way, data from
one source can be send to several frame grabbers either to enhance the
computing capacity by bringing in several computers, or to establish a
failsafe system.

The bandwidth of a single CameraLink HS link routed through one wire
pair depends on the technology used. Thus, the maximum bandwidth
of a link between frame grabber and camera is the result of the specified
bit rate and the number of available data lanes. On the first
configuration level with 4 links CameraLink HS uses a so-called passive
CX4 cable with a cable length of up to 20 m. At the time of writing it is
proving challenging to deliver extremely high flex versions of this cable.
The standard also defines the use of fibre giving extended cable lengths
of many hundreds of metres and there are also plans to offer a
CameraLink HS interface with only one line to serve the low-end
segment. With the challenge of making a high flex cable we expect
further cable configurations to follow. The integration of the power
supply source is a possibility, but not a reality in the early products
currently available.

To document the compatibility and the features of the different configuration levels of a CameraLink HS product there is a CLHS capability
designator for every product, which is composed as follows:

Capability designator: A-B, CDE|CDE, F

Field

Long description

Short description

A

Number of connectors for video transmission

QuantityConnector

B

Connector type

ConnectorType

C

Maximum number of data lanes in the cable

#DataLanes

D

Protocol type

Link Protocol

E

Number of command channels

#CommandChannels

F

Bit transfer rate

Transfer Speed

For example: "C2,7M1, S3" designates the following:

Erstes Feld leer

If the first field is left blank, then a single connector isdesignated

»C2«

The connector type is a copper, SFF-8470 withthumbscrew retention

»7«

Supports up to seven lanes of data

»M«

Protocol is multi-camera, multi-lane

»1«

Supports a single command channel

»S3«

Bitrate is 3,125 Gb/s. (Can be left blank if 3,125 Gb/sis the connector's default rate)

CameraLink HS resides under the management of the AIA, the
Automated Imaging Association. Like CoaXPress, this standard was
adopted by the G3 consortium of AIA, EMVA and JIIA, the worlds three
machine vision trade associations covering all continents. For more
information see http://www.machinevisiononline.org.